Radio base station, user terminal, radio communication method and radio communication system

ABSTRACT

A user terminal includes a receiving section that receives a signal subjected to multiplexing in a power dimension in a given layer and that receives information about the multiplexing in the power dimension; and a signal processing section that demodulates a signal for the user terminal from the multiplexed signal based on the information about the multiplexing in the power dimension.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of and, thereby,claims benefit under 35 U.S.C. § 120 to U.S. patent application Ser. No.14/655,526 filed on Jun. 25, 2015, titled, “RADIO BASE STATION, USERTERMINAL, RADIO COMMUNICATION METHOD AND RADIO COMMUNICATION SYSTEM,”which is a national stage application of PCT Application No.PCT/JP2013/084713, filed on Dec. 25, 2013, which claims priority toJapanese Patent Application No. 2012-288167 filed on Dec. 28, 2012. Thecontents of the priority applications are incorporated by reference intheir entirety.

TECHNICAL FIELD

The present invention relates to a radio base station, a user terminal,a radio communication method and a radio communication system.

BACKGROUND ART

The specifications of long-term evolution (LTE) have been developed forthe purpose of achieving increased speed, lower delay and so on in UMTS(Universal Mobile Telecommunications System) (non-patent literature 1).In LTE, a communication scheme that is based on OFDMA (OrthogonalFrequency Division Multiple Access) is used in downlink channels(downlink), and a communication scheme that is based on SC-FDMA (SingleCarrier Frequency Division Multiple Access) is used in uplink channels(uplink).

In LTE, MIMO (Multiple Input Multiple Output) transmission to transmitdifferent information data sequences in parallel from a plurality oftransmitting antennas by using the same radio resources (frequency band,time slots, etc.) is employed. In this MIMO transmission, a plurality ofinformation data sequences are transmitted via varying routes using thesame radio resources, so that it is possible to achieve high throughputand system capacity by space division multiplexing.

CITATION LIST Non-Patent Literature

Non-Patent Literature 1:3GPP TR 25.913 “Requirements for Evolved UTRAand Evolved UTRAN”

SUMMARY OF THE INVENTION Technical Problem

The throughput and system capacity that are achieved by above MIMOtransmission depend on the number of information data sequences to betransmitted in parallel. Consequently, if the number of information datasequences to be transmitted in parallel is increased by, for example,increasing the number of antennas pertaining to transmission/reception,it is possible to improve the throughput and system capacity. However,with this method, the system structure becomes more complex as thenumber of antennas increases, and therefore the throughput and systemcapacity that can be achieved are limited.

The present invention has been made in view of the above, and it istherefore an object of the present invention to provide a radio basestation, a user terminal, a radio communication method and a radiocommunication system of novel structures that can achieve improvedthroughput and system capacity.

Solution to Problem

A radio base station according to the present invention has a beamgenerating section that generates a plurality of transmission beams, adownlink reference signal generating section that generates downlinkreference signals that are specific to each transmission beam, adownlink control information generating section that generates downlinkcontrol information to request a feedback of channel state informationto a user terminal, a scheduling section that determines a plurality ofuser terminals to non-orthogonal-multiplex, per transmission beam, basedon the channel state information that is fed back, and a downlinkchannel multiplexing section that non-orthogonal-multiplexes downlinksignals for the plurality of user terminals that are determined, in eachof the plurality of transmission beams, in accordance with resultsdetermined in the scheduling section.

Technical Advantage of the Invention

According to the present invention, it is possible to provide a radiobase station, a user terminal, a radio communication method and a radiocommunication system of novel structures that can achieve improvedthroughput and system capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram to show an example basic structure of aradio communication system where MIMO transmission is employed;

FIG. 2 is a schematic diagram to show an example basic structure of aradio communication system where NOMA is employed;

FIGS. 3A and 3B provide schematic diagrams to show an example structureof a radio communication system where opportunistic beamforming isemployed;

FIG. 4 is a graph to show the relationship between the number of userterminals and average throughput;

FIGS. 5A and 5B provide schematic diagrams to explain a radiocommunication scheme according to the present embodiment;

FIG. 6 is a schematic diagram to show an example radio resourcestructure of downlink reference signals that are transmitted from aradio base station;

FIG. 7 is a schematic diagram to explain how downlink signals that aretransmitted by non-orthogonal multiplexing are received in each userterminal;

FIGS. 8A and 8B provide schematic diagrams to show example transmissionschemes that are supported by the radio communication scheme of thepresent embodiment;

FIGS. 9A-9D provide schematic diagrams to show example radio resourcestructures of demodulation reference signals that are transmitted from aradio base station;

FIG. 10 is a flow chart to show a control flow on the radio base stationside;

FIG. 11 is a flow chart to show a control flow on the user terminalside;

FIG. 12 is a schematic diagram to show an example structure of a radiocommunication system according to the present embodiment;

FIG. 13 is a block diagram to show an example structure of a radio basestation according to the present embodiment;

FIG. 14 is a block diagram to show an example structure of a userterminal according to the present embodiment; and

FIG. 15 is a block diagram to show example structures of baseband signalprocessing sections provided in a radio base station and a user terminalaccording to the present embodiment.

DESCRIPTION OF EMBODIMENTS

FIG. 1 is a schematic diagram to show an example basic structure of aradio communication system where MIMO (Multiple Input Multiple Output)transmission is employed. The radio communication system shown in FIG. 1has radio base station eNB #1 (eNB: eNodeB) with a plurality oftransmitting antennas. In the coverage area of radio base station eNB#1, a plurality of user terminals UE #1 (UE: User Equipment) (here, userterminals UE #1A, UE #1B and UE #1C) are present.

In this radio communication system, different data sequences aretransmitted from a plurality of antennas of radio base station eNB #1 toa plurality of user terminals UE #1 in parallel. That is, a plurality ofinformation data sequences are transmitted by using the same radioresources, in different routes. Examples of MIMO transmission includesingle-user MIMO (SU-MIMO) transmission to transmit a plurality ofinformation data sequence to a single user terminal UE #1 in parallel,and multiple-user MIMO (MU-MIMO) transmission to transmit a plurality ofinformation data sequences to different user terminals UE #1 inparallel. FIG. 1 shows a case where multi-user MIMO transmission isemployed.

The throughput and system capacity of a radio communication systememploying MIMO transmission depend on the number of information datasequences that are transmitted in parallel. That is, if the number ofinformation data sequences to be transmitted in parallel is increasedby, for example, increasing the number of antennas in radio base stationeNB #1 and user terminal UE #1, it is possible to improve the throughputand system capacity of the radio communication system. However, if thenumber of information data sequences to be transmitted in parallel isincreased, the system structure that is required fortransmission/reception becomes complex, and, in the future, it becomesnecessary to improve throughput and system capacity in a differentapproach from the space division multiplexing (space dimensionmultiplexing) of above MIMO transmission.

For example, it is possible to improve the throughput and systemcapacity of a radio communication system even more by employingnon-orthogonal access, whereby downlink transmission power (transmissionpower) is changed per user terminal UE #1 (and which is also referred toas “non-orthogonal multiplexing,” “power division multiplexing,” “powerdimension multiplexing” and so on). So, a study has been conducted onNOMA (Non-Orthogonal Multiple Access), which is non-orthogonal accesspremised upon canceling interference on the receiving side.

FIG. 2 is a schematic diagram to show an example basic structure of aradio communication system employing NOMA. FIG. 2 shows an example inwhich radio base station eNB #2 forms a cell. In the coverage area ofradio base station eNB #2, a plurality of user terminals UE #2 (here,user terminals UE #2A, UE #2B and UE #2C) are placed. In this radiocommunication system, downlink data signals are transmitted withdifferent transmission power from the transmitting antennas of radiobase station eNB #2 to a plurality of user terminals UE #2.

In the radio communication system shown in FIG. 2, transmission power iscontrolled in accordance with, for example, the received SINR of userterminal UE #2, the path loss (propagation loss and route loss) betweenradio base station eNB #2 and user terminal UE #2, and so on. To be morespecific, control is executed so that low transmission power isallocated to user terminal UE #2A where the received SINR is high (thepath loss is insignificant), and high transmission power is allocated touser terminal UE #2C where the received SINR is low (the path loss issignificant).

When transmission power is allocated in such a manner, signals for userterminals UE #2A and UE #2B become sufficiently weak in the locationwhere user terminal UE #2C serves. Consequently, user terminal UE #2Ccan decode the signal for user terminal UE #2C assuming that there islittle interference from the signals for user terminals UE #2A and UE#2B. Signals for user terminals UE #2B and UE #2C are strong in thelocation where user terminal UE #2A serves. Consequently, user terminalUE #2A receives the signals for user terminals UE #2B and UE #2C, inaddition to the signal for user terminal UE #2A.

In NOMA, signals for each user terminal UE #2 are multiplexed in anidentifiable manner. User terminal UE #2A decodes the signals for userterminals UE #2B and UE #2C by means of SIC (Successive InterferenceCancellation), and separates the signal for user terminal UE #2A. Byapplying this NOMA and multiplexing (non-orthogonal-multiplexing)signals for a plurality of user terminals UE #2 over the same radioresources (frequency band, time slots, etc.) with different transmissionpower, it may be possible to improve the throughput and system capacityeven more.

Now, the affinity between SIC used in NOMA, and MIMO transmission willbe considered. For example, assume that, in the system structure shownin FIG. 1, h₁=[100 99] is the channel matrix to represent the channelstate between radio base station eNB #1 and user terminal UE #1A andh₂=[1−1] is the channel matrix to represent the channel state betweenradio base station eNB #1 and user terminal UE #1B. When precoding iscarried out using a precoder m₂=[1−1]^(T), h₁·m₂=1<h₂·m₂₌₂ holds, sothat the received signal intensity in user terminal UE #1A becomes lowerthan the received signal intensity in user terminal UE #1B. Whenprecoding is carried out using a precoder m₂=[1]^(T), h₁·m₂=199>h₂·m₂=0holds, so that the received signal intensity in user terminal UE #1Abecomes greater than the received signal intensity in user terminal UE#1B.

In this way, in MIMO transmission, the signal intensity as received inuser terminals UE #1 varies depending on the precoder that is applied,so that it is not possible to uniquely determine whether the channelstate is good or poor. Consequently, there is a possibility that, withtransmission power control alone, signals for other user terminals UE#1, which cause interference, cannot be decoded or cancelled. That is,in MIMO transmission, a downlink communication channel cannot be handledas a degraded BC (Broadcast Channel), and therefore it is not possibleto uniquely determine whether the channel state is good or poor, andthis makes it difficult to apply above-noted SIC.

The above problem can be solved by employing precoding (for example, THP(Tomlinson Harashima Precoding)) by means of DPC (Dirty Paper Coding).However, in that case, the system structure becomes complex. Also,precoding by means of DPC is sensitive to the quality of channel stateinformation (CSI) that is provided as feedback, and therefore there isalso a problem that the quality of communication is even more likely tolower due to the influence of the decrease of the accuracy of channelestimation, feedback errors, and so on.

Given these problems, the present inventors have thought that it may bepossible to achieve improved throughput and system capacity, by applyingnon-orthogonal multiplexing (NOMA) to system structures in which adownlink communication channel can be handled as a degraded BC, in MIMOtransmission to use a plurality of transmitting/receiving antennas,without making the structure complex. As for the system structures inwhich a downlink communication channel can be handled as a degraded BC,for example, a system structure to employ opportunistic beamforming ispossible. Note that opportunistic beamforming may be referred to as“random beamforming” as well.

FIG. 3 provides schematic diagrams to show an example structure of aradio communication system where opportunistic beamforming is employed.The radio communication system shown in FIG. 3A has radio base stationeNB #3 that generates transmission beams B1, B2 and B3 of predeterminedpatterns or random patterns. A plurality of transmission beams B1, B2and B3 that are generated in radio base station eNB #3 are, for example,made orthogonal to each other. However, since the interference betweenthe transmission beams can be canceled by an IRC (Interference RejectionCombining) receiver of a linear filter and/or the like on the receivingside, it is not necessary to make these transmission beams completelyorthogonal to each other. In this opportunistic beamforming, as shown inFIG. 3B, the transmission beams B1, B2 and B3 are generated by usingradio resources (frequency band, time slots. etc.) of predeterminedpatterns or random patterns. Note that, in opportunistic beamforming, aplurality of transmission beams have only to be generated using radioresources of predetermined patterns, so that the number of transmissionbeams generated at a given time (time slot) may be one.

A plurality of user terminals UE #3 are placed in each of the coverageareas of transmission beams B1, B2 and B3. Each user terminal UE #3performs channel estimation based on beam-specific downlink referencesignals transmitted in each transmission beam B1, B2 and B3, and feedsback channel quality information (CQI: Channel Quality Indicator) toradio base station eNB #3. Radio base station eNB #3 transmits downlinkdata by selecting user terminal UE #3 of the highest CQI amongtransmission beams B1, B2 and B3.

FIG. 4 is a graph to show the relationship between the number of userterminals and average throughput. In opportunistic beamforming (Opp. BF:Opportunistic BeamForming), as noted earlier, downlink data istransmitted by selecting user terminal UE #3 of the highest CQI in thecoverage areas of transmission beams B1, B2 and B3, which are generatedin arbitrary patterns. If the number of user terminals UE #3 in eachcoverage area increases, the possibility that user terminal UE #3 ofgood channel quality are present also increases, so that, as shown inFIG. 4, it is possible achieve high throughput that is as good as thatof above-described MIMO transmission (Coherent BF: CoherentBeamForming).

In this opportunistic beamforming, for example, it is possible to handlea communication channel as a degraded BC by canceling the interferenceamong transmission beams B1, B2 and B3 by means of a linear filter.Consequently, the affinity with SIC is high, and it is possible tocancel interference adequately even when non-orthogonal multiplexing isemployed. So, with the present invention, non-orthogonal multiplexing isapplied to this opportunistic beamforming. Now, the present inventionwill be described below.

FIG. 5 provides schematic diagrams to explain the radio communicationscheme according to the present embodiment. The radio communicationsystem shown in FIG. 5A has radio base station eNB #5, which generates Ntransmission beams, beam #1 to beam #N, of predetermined patterns orrandom patterns. The N transmission beams, beam #1 to beam #N, generatedin radio base station eNB #5, are made orthogonal to each other. In thisradio communication system, transmission beams beam #1 to beam #N aregenerated by using radio resources (frequency band, time slots, etc.) ofpredetermined patterns or random patterns.

In each of the coverage areas of transmission beams beam #1 to beam #N,a plurality of user terminals UE #5 are placed. Radio base station eNB#5 transmits downlink reference signals (CSI-RSs (Channel StateInformation Reference Signals), DM-RSs (DeModulation Reference Signals)and so on), which are specific to each of transmission beams beam #1 tobeam #N, to a plurality of user terminals UE #5. FIG. 6 is a schematicdiagram to show an example radio resource structure of downlinkreference signals transmitted from a radio base station, illustrating acase where four transmission beams beam #1 to beam #4 are generated atthe same time. As shown in FIG. 6, downlink reference signals, which arespecific to each transmission beam, are multiplexed over, for example,the PDSCH (Physical Downlink Shared CHannel) region of each resourceblock (RB). As for the method of multiplexing reference signals for aplurality of user terminals UE #5 in each transmission beam, a referencesignal multiplexing method that is suitable for conventionalnon-orthogonal access multiplexing may be employed.

Each user terminal UE #5 performs channel estimation based on thebeam-specific downlink reference signals transmitted in eachtransmission beam beam #1 to beam #N, and feeds back channel qualityinformation (CQIs) to radio base station eNB #5. Radio base station eNB#5 determines the set of a plurality of user terminals UE #5 to benon-orthogonal-multiplexed in each transmission beam beam #1 to beam #N,based on the CQIs that are fed back. Note that the information to be fedback from each user terminal UE #5 is by no means limited to channelquality information (CQIs). At least, channel state information (CSI) torepresent channel states has to be fed back.

The set of a plurality of user terminals UE #5 to benon-orthogonal-multiplexed is determined based on an arbitraryscheduling metric so that the indicator values for user terminalselection such as the total sum rate are maximized. For example, in anarbitrary frequency block b, interference by all the users i thatsatisfy h_(i,b)/N_(i,b)<h_(k,b)/N_(k,b) can be canceled by user k's SIC,so that user k's throughput R^((sic))(k) can be represented by followingformula 1:

$\begin{matrix}{{R^{({sic})}(k)} = {\sum\limits_{b = 1}^{B}\;{W\;{\log_{2}( {1 + \frac{h_{k,b}P_{k,b}}{{\sum\limits_{{i = 1},{\frac{h_{k,b}}{N_{k,b}} < \frac{h_{i,b}}{N_{i,b}}}}^{K}\;{h_{k,b}P_{i,b}}} + {WN}_{k,b}}} )}}}} & \lbrack {{Formula}\mspace{14mu} 1} \rbrack\end{matrix}$

When scheduling to maximize the worst user throughput (minimumthroughput) is executed, it is possible to determine the set of aplurality of user terminals UE #5 to be non-orthogonal-multiplexed, bysolving the problem with optimal power allocation represented byfollowing formulas 2 and 3. K is the total number of user terminals, Bis the total number of transmission beams, and P is the sum value oftransmission power.

$\begin{matrix}{{maximize}\mspace{14mu}{\min\limits_{k}{R^{({sic})}(k)}}} & \lbrack {{Formula}\mspace{14mu} 2} \rbrack \\{{{{subject}\mspace{14mu}{to}\mspace{14mu} P_{k,b}} \geq 0},{\forall k},b,{{\sum\limits_{b = 1}^{B}\;{\sum\limits_{k = 1}^{K}\; P_{k,b}}} \leq P}} & \lbrack {{Formula}\mspace{14mu} 3} \rbrack\end{matrix}$

When the set of a plurality of user terminals UE #5 to benon-orthogonal-multiplexed in each transmission beam beam #1 to beam #Nis determined, radio base station eNB #5 non-orthogonal-multiplexes thedownlink signals for corresponding user terminals UE #5 in eachtransmission beam beam #1 to beam #N by superposition coding. That is,signals for a plurality of user terminals UE #5 are multiplexed over thesame radio resources (frequency band, time slots, etc.) by changing thetransmission power. Also, to each user terminal #5, information of otheruser terminals #5, which is necessary upon interference cancelation bySIC, is reported.

As shown in FIG. 5B, in part of the frequency bands f1, downlink signalsto correspond to the set of a plurality of user terminals UE #5 of eachtransmission beam beam #1 to beam #N are non-orthogonal-multiplexed. Forexample, in FIG. 5B, downlink signals for user terminals UE #5A, UE #5Band UE #5C are non-orthogonal-multiplexed in the frequency band f1 oftransmission beam beam #1. Also, downlink signals for user terminals UE#5H, UE #51 and UE #5J are non-orthogonal-multiplexed in the frequencyband f1 of transmission beam beam #N.

Note that other signals (downlink signals or uplink signals) aremultiplexed in the frequency bands f2 of transmission beams beam #1 tobeam #N. In this way, although FIG. 5B shows a radio resource structure(orthogonal/non-orthogonal hybrid multiple access) which combinesorthogonal multiplexing and non-orthogonal multiplexing by frequencybands f1 and f2, it is equally possible to apply non-orthogonalmultiplexing alone to the whole frequency band.

In each transmission beam beam #1 to beam #N, the transmission power ofthe signals to be non-orthogonal-multiplexed is determined based on CQIs(or CSI) that are fed back. For example, as shown in FIG. 5B, intransmission beam beam #1, radio base station eNB #5 minimizes thetransmission power for user terminal UE #5A having the highest receivedSINR (the lowest path loss), and maximizes the transmission power foruser terminal UE #5C having the lowest received SINR (the largest pathloss). Also, in transmission beam beam #N, radio base station eNB #5minimizes the transmission power for user terminal UE #5H having thehighest received SINR (the lowest path loss), and maximizes thetransmission power for user terminal UE #5J having the lowest receivedSINR (the largest path loss).

FIG. 7 is a schematic diagram to explain how downlink signals that aretransmitted by non-orthogonal multiplexing are received in each userterminal. In FIG. 7, the received SINR at user terminal UE #7B is lowerthan the received SINR at user terminal UE #7A. Alternatively, the pathloss between radio base station eNB #7 and user terminal UE #7B isgreater than the path loss between radio base station eNB #7 and userterminal UE #7A. Consequently, radio base station eNB #7 configures thetransmission power for user terminal UE #7A where the received SINR ishigh (the path loss is low) lower than the transmission power for userterminal UE #7B where the received SINR is low (the path loss is high).

In the location where user terminal UE #7B serves, the signal for userterminal UE #7A becomes sufficiently weak. Consequently, user terminalUE #7B can decode the signal for user terminal UE #7B assuming thatthere is little interference from the signal for user terminal UE #7A.The signal for user terminal UE #7B is strong in the location where userterminal UE #7A serves. Consequently, user terminal UE #7A receives thesignal for user terminal UE #7B in addition to the signal for userterminal UE #7A.

The signals for user terminal UE #7A and UE #7B are multiplexed in anidentifiable manner. Consequently, user terminal UE #7A cancels thesignal for user terminal UE #7B by SIC and separates the signal for userterminal UE #7A. As a result of this, user terminal UE #7A can decodethe signal for user terminal UE #7A. The same holds with user terminalsUE #7C and UE #7D. That is, user terminal UE #7D assumes decodes thesignal for user terminal UE #7D assuming that there is littleinterference from the signal for user terminal UE #7C. User terminal UE#7C cancels the signal for user terminal UE #7D by SIC, and separatesand decodes the signal for user terminal UE #7C.

The above-described SIC is employed to cancel signals for user terminalsUE where the condition of the transmission path is poorer (the receivedSINR is lower or the path loss is greater) than at the subject terminal.Signals for user terminals UE where the condition of the transmissionpath is poorer than at the subject terminal are transmitted with higherpower than the signal for the subject terminal, and therefore can bedecoded properly at the subject terminal. Consequently, interference bysignals for such user terminals UE is adequately canceled by means ofSIC. Signals for user terminals UE where the condition of thetransmission path is better than at the subject terminal are transmittedwith lower transmission power than the signal for the subject terminal,so that the interference can be ignored.

With the radio communication scheme of the present embodiment structuredin this way, a transmission signal vector x can be represented byfollowing formula 4. B is the total number of transmission beams, m_(b)is the beam vector (precoder) of the b-th transmission beam, P_(b,u) isthe transmission power for the u-th user terminal that issuperposition-coded in the b-th transmission beam, and s_(b,u) is thesignal for the u-th user terminal that is superposition-coded in theb-th transmission beam.

$\begin{matrix}{x = {\sum\limits_{b = 1}^{B}{m_{b}{\sum\limits_{u = 1}^{n{(b)}}\;{\sqrt{P_{b,u}}s_{b,u^{\prime}}}}}}} & \lbrack {{Formula}\mspace{14mu} 4} \rbrack\end{matrix}$

Also, following formula 5 holds. P_(b)′ is the transmission power of theb-th transmission beam, and P is the sum value of the transmission powerof all transmission beams.

$\begin{matrix}{{\sum\limits_{u = 1}^{n{(b)}}P_{b,u}} = {{P_{b^{\prime}}{\sum\limits_{b = 1}^{B}P_{b}}} = P}} & \lbrack {{Formula}\mspace{14mu} 5} \rbrack\end{matrix}$

Also, the received signal vector y_(b,u) of the u-th user terminal thatis superposition-coded in the b-th transmission beam is represented byfollowing formula 6. H_(b,u) is the channel matrix for the u-th userterminal that is superposition-coded in the b-th transmission beam, andw_(b,u) is the vector of the noise/interference against the u-th userterminal that is superposition-coded in the b-th transmission beam.

$\begin{matrix}{y_{b,u} = {{{H_{b,u}x} + w_{b,u}} = {{H_{b,u}{\sum\limits_{b^{\prime} = 1}^{B}{m_{b^{\prime}}{\sum\limits_{u^{\prime} = 1}^{n{(b^{\prime})}}{\sqrt{P_{b^{\prime},u^{\prime}}}s_{b^{\prime},u^{\prime}}}}}}} + w_{b,u}}}} & \lbrack {{Formula}\mspace{14mu} 6} \rbrack\end{matrix}$

Interference between the transmission beams can be suppressed by meansof receiving linear filtering, not by SIC. Considering this, a receivedsignal vector y˜_(b,u) after the filtering of the u-th user terminalthat is superposition-coded in the b-th transmission beam is representedby following formula 7. V^(H) _(b,u) is the receiving filter vector ofthe u-th user terminal that is superposition-coded in the b-thtransmission beam.

$\begin{matrix}{{\overset{\sim}{y}}_{b,u} = {{v_{b,u}^{H}y_{b,u}} = {{v_{b,u}^{H}H_{b,u}m_{b}{\sum\limits_{u^{\prime} = 1}^{n{(b)}}\;{\sqrt{P_{b,u^{\prime}}}s_{b,u^{\prime}}}}} + {v_{b,u}^{H}H_{b,u}{\sum\limits_{{b^{\prime} = 1}{b^{\prime} \neq b}}^{B}{m_{b^{\prime}}{\sum\limits_{u^{\prime} = 1}^{n{(b^{\prime})}}\;{\sqrt{P_{b^{\prime},u^{\prime}}}s_{b^{\prime},u^{\prime}}}}}}}}}} & \lbrack {{Formula}\mspace{14mu} 7} \rbrack\end{matrix}$

Following formula 8 is an equivalent channel representation to aboveformula 7. w˜_(b,u) is the power noise against the u-th user terminalthat is superposition-coded in the b-th transmission beam. g_(b,u) isrepresented by following formula 9.

$\begin{matrix}{{\overset{\sim}{y}}_{b,u} = {{g_{b,u}{\sum\limits_{u^{\prime} = 1}^{n{(b)}}{\sqrt{P_{b,u^{\prime}}}s_{b,u^{\prime}}}}} + \overset{\sim}{w_{b,u}}}} & \lbrack {{Formula}\mspace{14mu} 8} \rbrack \\{g_{b,u} = \sqrt{\frac{{{v_{b,u}^{H}H_{b,u}m_{b}}}^{2}}{{\sum\limits_{{b^{\prime} = 1}{b^{\prime} \neq 1}}^{B}{P_{b^{\prime}}{{v_{b,u}^{H}H_{b,u}m_{b^{\prime}}}}^{2}}} + {v_{b,u}^{H}{E\lbrack {w_{b,u}w_{b,u}^{H}} \rbrack}v_{b,u}}}}} & \lbrack {{Formula}\mspace{14mu} 9} \rbrack\end{matrix}$

It is clear, from above formula 8, that a downlink communication channelcan be seen as a degraded BC. Consequently, with the radio communicationscheme of the present embodiment, interference in each transmission beamcan be adequately suppressed by means of receiving SIC.

As noted earlier, although NOMA is applied to MU-MIMO transmissionaccording to the radio communication scheme of the present embodiment,other transmission schemes are supported as well. FIG. 8 providesschematic diagrams to show examples of transmission schemes that aresupported by the radio communication scheme of the present embodiment.FIG. 8A shows an example of SU-MIMO transmission, and FIG. 8B shows anexample of transmission diversity. By allowing a radio communicationsystem to support the SU-MIMO transmission of FIG. 8A, it is possible toincrease the peak rate. Also, for example, in an application environmentwhere the precoding gain is little, the transmission diversity of FIG.8B is effective.

FIG. 9 provides schematic diagrams to show examples of radio resourcestructures of demodulation reference signals (DM-RSs) that aretransmitted from a radio base station. In FIG. 9A to FIG. 9D, thehorizontal axis is the radio resources (time and frequency), and thevertical axis is the transmission power. As shown in FIG. 9A, when NOMAis applied to transmission beams by one transmitting antenna, signalsfor each user terminal UE #9 are transmitted using the same radioresources, with different power. In this case, a DM-RS that is commonbetween user terminals UE #9 can be used as a reference signal fordemodulation. Also, as shown in FIG. 9B, in SU-MIMO transmission to usetransmission beams by a plurality of transmitting antennas (here, twotransmitting antennas TX1 and TX2), a plurality of (two) informationdata sequences (layers) for user terminal UE #9A are multiplexed overthe same radio resources. In this case, for example, DM-RSs that areorthogonal between the layers can be used as reference signals fordemodulation.

As shown in FIG. 9C, when NOMA is applied to SU-MIMO transmission wheretransmission beams by a plurality of transmitting antennas (here, twotransmitting antennas TX1 and TX2) are used, a plurality of (two)information data sequences (layers) for each user terminal UE #9 aremultiplexed over the same radio resources. Here, the signals for userterminals UE #9 are transmitted with different power. In this case, forexample, DM-RSs that are common between the user terminals in the samelayer and that are orthogonal between the layers can be used asreference signals for demodulation.

Furthermore, as shown in FIG. 9D, when NOMA is applied to MU-MIMOtransmission where transmission beams by a plurality of transmittingantennas (here, two transmitting antennas TX1 and TX2) are used, signalsfor each user terminal UE #9 are multiplexed over the same radioresources. In the same transmission beam, signals for each user terminal#9 are transmitted with different power. In this case, for example,DM-RSs that are common between user terminals UE #9 in the sametransmission beam and that are orthogonal between the transmission beamscan be used as reference signals for demodulation. When a DM-RSstructure that is common between user terminals is employed in this way,the transmission power ratio for each user terminal is reported. Notethat, although cases have been shown here where DM-RS structures thatare common between user terminals are employed, it is equally possibleto employ structures in which dedicated DM-RSs are transmitted on a peruser terminal basis.

Control flows of the radio communication scheme of the presentembodiment will be described. FIG. 10 is a flow chart to show thecontrol flow on the radio base station side. The radio base station eNBfirst determines the beam vectors (precoders) of the transmission beamsto use in data transmission (step ST11). For example, when twotransmitting antennas are used, two orthogonal beam vectors aregenerated randomly. Then, using transmission beams that are pre-codedwith each beam vector, downlink reference signals that are specific toeach transmission beam are transmitted to user terminals UE (step ST12).

Next, the radio base station eNB requests all the user terminals UE tofeed back CQIs based on the downlink reference signals transmitted ineach transmission beam (step ST13). For example, the radio base stationeNB commands the user terminals UE to feed back CQIs alone (which areequivalent to the SINR). In this case, it is possible to reduce theoverhead pertaining to feedback. However, the information to feed backis by no means limited to CQIs. At least, CSI to represent channelstates has only to be fed back. Note that, in this feedback,interference from other cells (other radio base stations eNB) is takeninto consideration.

When CQIs are fed back from the user terminals UE, the radio basestation eNB schedules each transmission beam based on the CQIs fed back,and determines the user terminals UE to non-orthogonal-multiplex (stepST14). That is, the radio base station eNB selects the user terminals UEto be subject to frequency scheduling, and determines the user terminalsUE to be subject to non-orthogonal multiplexing. The user terminals UEto be subject to non-orthogonal multiplexing are determined based on,for example, the above-mentioned scheduling metric.

After that, the radio base station eNB generates transmission signalsbased on scheduling information and information about the user terminalsto non-orthogonal-multiplex, and non-orthogonal-multiplexes andtransmits these transmission signals in each transmission beam (stepST15). Also, the radio base station eNB reports, to each user terminalUE, information about the other user terminals UE to benon-orthogonal-multiplexed in the same transmission beam (step ST16).This reporting is made by using, for example, higher layer signaling(RRC signaling and so on), signaling by PDCCH control information and soon.

FIG. 11 is a flow chart to show the control flow on the user terminalside. A user terminal UE receives the downlink reference signalstransmitted in each transmission beam (step ST21), and calculates andfeeds back CQIs to the radio base station eNB (step ST22). Note that theinformation to feed back is preferably CSI that represents the channelstates.

After that, the user terminal UE receives the transmission signalstransmitted from the radio base station eNB with control information(step ST23), and acquires information for the subject terminal andinformation for the other user terminals UE that arenon-orthogonal-multiplexed with the subject terminal in the sametransmission beam (step ST24). Also, the user terminal UE estimates CSIinformation with respect to the subject terminal by way of channelestimation (step ST25). The user terminal UE estimates CSI informationwith respect to the other user terminals UE based on the referencesignals for the other user terminals UE reported (step ST25).

After that, the user terminal UE cancels the interference between thetransmission beams by using a linear filter such as MMSE and IRC (stepST26). For example, in a structure to use two receiving antennas,interference between transmission beams is canceled by using an IRCreceiver or an MMSE receiver of a linear filter. Next, interference bysignals for the other user terminals that are non-orthogonal-multiplexedin the same transmission beam is canceled by means of SIC (step ST27).Here, SIC is employed to cancel the signals for user terminals UE wherethe condition of the transmission path is poorer (the received SINR islower or the path loss is greater) than at the subject terminal. Signalsfor user terminals UE where the condition of the transmission path ispoorer than at the subject terminal are transmitted with higher powerthan the signals for the subject terminal, and therefore can be decodedproperly at the subject terminal. Consequently, interference by signalsfor such user terminals UE is adequately canceled by means of SIC.Signals for user terminals UE where the condition of the transmissionpath is better (the received SINR is higher or the path loss is lower)than at the subject terminal are transmitted with lower transmissionpower than the signals for the subject terminal, so that theinterference can be ignored. After having canceled the interference bythe signals for the other user terminals UE, the user terminal UEdemodulates the user data for the subject terminal (step ST28).

In this way, with the radio communication scheme according to thepresent embodiment, non-orthogonal multiplexing is applied toopportunistic beamforming, which can achieve equivalent systemcharacteristics to MIMO transmission, so that it is possible to improvethe throughput and system capacity even more.

Now, the radio communication system according to the present embodimentwill be described below in detail. FIG. 12 is a schematic diagram toshow an example structure of the radio communication system according tothe present embodiment. Note that the radio communication system shownin FIG. 12 is a system to accommodate, for example, the LTE system orthe LTE-A (LTE-Advanced) system. This radio communication system may bereferred to as “beyond IMT-advanced,” or may be referred to as “beyond4G.”

As shown in FIG. 12, the radio communication system 1 includes radiobase stations 10 (10A and 10B), and a plurality of user terminals 20(20A and 20B) that communicate with these radio base stations 10. Theradio base stations 10 are connected with a higher station apparatus 30,and this higher station apparatus 30 is connected with a core network40. Each user terminal 20 can communicate with the radio base stations10 in cells C1 and C2. The user terminals 20 may be mobile terminals ormay be fixed terminals. Note that the higher station apparatus 30 maybe, for example, an access gateway apparatus, a radio network controller(RNC), a mobility management entity (MME) and so on, but is by no meanslimited to these.

In the radio communication system 1, as radio access schemes, OFDMA(Orthogonal Frequency Division Multiple Access) is applied to thedownlink, and SC-FDMA (Single-Carrier Frequency Division MultipleAccess) is applied to the uplink. OFDMA is a multi-carrier transmissionscheme to perform communication by dividing a frequency band into aplurality of narrow frequency bands (subcarriers) and mapping data toeach subcarrier. SC-FDMA is a single-carrier transmission scheme toreduce interference between terminals by dividing the system band intobands formed with one or continuous resource blocks, per terminal, andallowing a plurality of terminals to use mutually different bands.

Here, communication channels to be used in the radio communicationsystem 1 shown in FIG. 12 will be described. Downlink communicationchannels include a PDSCH (Physical Downlink Shared CHannel), which isused by each user terminal 20 on a shared basis, and downlink L1/L2control channels (PDCCH, PCFICH, PHICH and enhanced PDCCH). User dataand higher control information are transmitted by the PDSCH. Schedulinginformation for the PDSCH and the PUSCH and so on are transmitted by thePDCCH (Physical Downlink Control CHannel). The number of OFDM symbols touse for the PDCCH is transmitted by the PCFICH (Physical Control FormatIndicator CHannel). HARQ ACK and NACK for the PUSCH are transmitted bythe PHICH (Physical Hybrid-ARQ Indicator CHannel).

Uplink control channels include the PUSCH (Physical Uplink SharedCHannel), which is used by each user terminal 20 on a shared basis as anuplink data channel, and the PUCCH (Physical Uplink Control CHannel),which is an uplink control channel. User data and higher controlinformation are transmitted by this PUSCH. Also, by means of the PUCCH,downlink channel quality information (CQI: Channel Quality Indicator),ACK/NACK and so on are transmitted.

FIG. 12 is a block diagram to show an example structure of a radio basestation according to the present embodiment. A radio base station has aplurality of transmitting/receiving antennas 101 for opportunisticbeamforming, amplifying sections 102, transmitting/receiving sections103, a baseband signal processing section 104, a call processing section105 and a transmission path interface 106.

User data to be transmitted from the radio base station 10 to a userterminal 20 on the downlink is input from the higher station apparatus30, into the baseband signal processing section 104, via thetransmission path interface 106.

In the baseband signal processing section 104, user data that is inputis subjected to a PDCP layer process, division and coupling of userdata, RLC (Radio Link Control) layer transmission processes such as anRLC retransmission control transmission process, MAC (Medium AccessControl) retransmission control, including, for example, an HARQtransmission process, scheduling, transport format selection, channelcoding, an inverse fast Fourier transform (IFFT) process and a precodingprocess, and then transferred to each transmitting/receiving section103. Furthermore, downlink control information is subjected totransmission processes such as channel coding and an IFFT process, andtransferred to each transmitting/receiving section 103.

Also, the baseband signal processing section 104 reports controlinformation for communication in the serving cell to the user terminals20 through a broadcast channel. The information for communication in theserving cell includes, for example, the uplink or downlink systembandwidth.

Each transmitting/receiving section 103 converts the baseband signals,which are pre-coded and output from the baseband signal processingsection 104 on a per antenna basis, into a radio frequency band. Theamplifying sections 102 amplify the radio frequency signals having beensubjected to frequency conversion, and transmit the results through thetransmitting/receiving antennas 101.

Data to be transmitted from the user terminal 20 to the radio basestation 10 on the uplink is received in each transmitting/receivingantenna 101 and input in the amplifying sections 102. Radio frequencysignals that are input from each transmitting/receiving antenna 101 areamplified in the amplifying sections 102 and sent to eachtransmitting/receiving section 103. The amplified radio frequencysignals are converted into baseband signals in eachtransmitting/receiving section 103, and input in the baseband signalprocessing section 104.

In the baseband signal processing section 104, user data that isincluded in the baseband signals that are input is subjected to aninverse fast Fourier transform (IFFT) process, an inverse discreteFourier transform (IDFT) process, error correction decoding, a MACretransmission control receiving process, and RLC layer and PDCP layerreceiving processes, and transferred to the higher station apparatus 30via the transmission path interface 106. The call processing section 105performs call processing such as setting up and releasing communicationchannels, manages the state of the radio base station 10 and manages theradio resources.

FIG. 14 is a block diagram to show an example structure of a userterminal according to the present embodiment. A user terminal 20 has aplurality of transmitting/receiving antennas 201, amplifying sections202, transmitting/receiving section 203, a baseband signal processingsection 204 and an application section 205.

Downlink data is received in a plurality of transmitting/receivingantennas 201 and input in the amplifying sections 202. The radiofrequency signals input from each transmitting/receiving antenna 201 areamplified in the amplifying sections 202 and sent to eachtransmitting/receiving section 203. The amplified radio frequencysignals are converted into baseband signals in eachtransmitting/receiving section 203, and input in the baseband signalprocessing section 204. In the baseband signal processing section 204,the baseband signals that are input are subjected to an FFT process,error correction decoding, a retransmission control receiving processand so on. User data that is included in the downlink data istransferred to the application section 205. The application section 205performs processes related to higher layers above the physical layer andthe MAC layer. Also, the broadcast information that is included in thedownlink data is also transferred to the application section 205.

Uplink user data is input from the application section 205 to thebaseband signal processing section 204. In the baseband signalprocessing section 204, the user data that is input is subjected to aretransmission control (H-ARQ (Hybrid ARQ)) transmission process,channel coding, precoding, a discrete Fourier transform (DFT) process,an IFFT process and so on, and then transferred to eachtransmitting/receiving section 203. Baseband signals that are outputfrom the baseband signal processing section 204 are converted into aradio frequency band in the transmitting/receiving sections 203. Afterthat, the radio frequency signals having been subjected to frequencyconversion are amplified in the amplifying sections 202 and transmittedfrom the transmitting/receiving antennas 201.

FIG. 15 is a block diagram to show example structures of the basebandsignal processing sections provided in the radio base stations and userterminals according to the present embodiment. Note that, although FIG.15 shows only part of the structures, the radio base station and theuser terminal 20 have components that are required, without shortage.

As shown in FIG. 15, the radio base station 10 has a beam generatingsection 301, a downlink control information generating section 302, adownlink control information coding/modulation section 303, a downlinktransmission data generating section 304, a downlink transmission datacoding/modulation section 305, a downlink reference signal generatingsection 306, a downlink channel multiplexing section 307 and ascheduling section 308.

The beam generating section 301 generates a plurality of transmissionbeams that are orthogonal to each other by using radio resources(frequency band, time slots, etc.) of predetermined patterns or randompatterns.

The downlink control information generating section 302 generates userterminal-specific (UE-specific) downlink control information (DCI) to betransmitted in the PDCCH. The user terminal-specific downlink controlinformation includes DL assignments, which are PDSCH allocationinformation, UL grants, which are PUSCH allocation information, and soon. Also, this downlink control information includes control informationto request a feedback of CQIs (or CSI) to each user terminal 20.

The downlink control information that is generated in the downlinkcontrol information generating section 302 is input in the downlinkcontrol information coding/modulation section 303, with shared controlinformation that is common between the user terminals, as downlinkcontrol information to be transmitted in the PDCCH. The downlink controlinformation coding/modulation section 303 performs channel coding andmodulation of the downlink control information that is input. Themodulated downlink control information is output to the downlink channelmultiplexing section 307.

The downlink transmission data generating section 304 generates downlinkuser data on a per user terminal 20 basis. The downlink user data thatis generated in the downlink transmission data generating section 304 isinput in the downlink transmission data coding/modulation section 305,with higher control information, as downlink transmission data to betransmitted in the PDSCH. The downlink transmission datacoding/modulation section 305 performs channel coding and modulation ofthe downlink transmission data for each user terminal 20. The modulateddownlink transmission data is output to the downlink channelmultiplexing section 307.

The downlink reference signal generating section 306 generates downlinkreference signals (CRSs (Cell-specific Reference Signals), CSI-RSs,DM-RSs and so on). The generated downlink reference signals are outputto the downlink channel multiplexing section 307. Note that, forexample, CSI-RSs that are specific to each transmission beam are used tomeasure CQIs (or CSI).

The downlink channel multiplexing section 307 combines the downlinkcontrol information, the downlink reference signals and the downlinktransmission data (including higher control information) and generatesdownlink signals (transmission signals). To be more specific, thedownlink channel multiplexing section 307 non-orthogonal-multiplexesdownlink signals, on a per transmission beam basis, for a plurality ofuser terminals 20 that are determined in the scheduling section 308, inaccordance with scheduling information reported from the schedulingsection 308. The downlink signals generated in the downlink channelmultiplexing section 307 undergo an inverse fast Fourier transformprocess, a precoding process and so on, and transferred to thetransmitting/receiving sections 103.

The scheduling section 308 generates scheduling information forcommanding allocation of radio resources to the downlink transmissiondata and the downlink control information, based on command informationfrom the higher station apparatus 30 and CSI (CQIs (Channel QualityIndicators), RIs (Rank Indicators) and so on) from each user terminal20. Also, the scheduling section 308 determines a plurality of userterminals UE to non-orthogonal-multiplex, per transmission beam, basedon the CQIs (or CSI) that are fed back.

In this radio base station 10, beam vectors (precoders) of thetransmission beams to be used in data transmission are determined in thebeam generating section 301. The transmission beam-specific downlinkreference signals (for example, CSI-RSs) that are generated in thedownlink reference signal generating section 306 are transmitted to theuser terminals 20 in the transmission beams corresponding to each beamvector. Also, control information to request a feedback of CQIs (or CSI)is generated in the downlink control information generating section 302,and transmitted to all the user terminals 20.

When CQIs (or CSI) are fed back from each user terminal 20, thescheduling section 308 schedule each transmission beam and determinesthe user terminals 20 to non-orthogonal-multiplex based on the CQIs fedback. Also, the downlink channel multiplexing section 307non-orthogonal-multiplexes downlink signals, per transmission beam, fora plurality of user terminals 20 determined in the scheduling section308, in accordance with scheduling information that is reported from thescheduling section 308. Also, the radio base station 10 reports, to eachuser terminal 20, information related to the other user terminals 20that are non-orthogonal-multiplexed in the same transmission beam.

As shown in FIG. 15, a user terminal 20 has a downlink controlinformation receiving section 401, a channel estimation section 402, afeedback section 403, an interference cancelation section 404 and adownlink transmission data receiving section 405.

A downlink signal that is sent out from the radio base station 10 isreceived in the transmitting/receiving antennas 201, undergoes removalof the cyclic prefixes, a fast Fourier transform process and so on, andthen transferred to the baseband signal processing section 204. Thedownlink signal is separated into the downlink control information, thedownlink transmission data (including higher control information), andthe downlink reference signals, in the baseband signal processingsection 204. The downlink control information is input in the downlinkcontrol information receiving section 401, the downlink transmissiondata is input in the downlink transmission data receiving section 405,and the downlink reference signals are input in the channel estimationsection 402.

In the downlink control information receiving section 401, the downlinkcontrol information is demodulated and output to the channel estimationsection 402, the feedback section 403, the interference cancelationsection 404 and so on. When a CQI (or CSI) feedback request is receivedvia the downlink control information, the channel estimation section 402performs channel estimation based on the transmission beam-specificdownlink reference signals (CSI-RSs and so on), and measures CQIs (orCSI). The CQIs (or CSI) that are acquired in the channel estimation arefed back to the radio base station 10 through the feedback section 403.

The interference cancelation section 404 cancels the interferencebetween the transmission beams by using a linear filter. Also, theinterference cancelation section 404 cancels the interference by signalsfor other user terminals 20, from the downlink signals for a pluralityof user terminals 20 that are non-orthogonal-multiplexed pertransmission beam. To be more specific, based on information of thesubject terminal and other user terminals 20 that is reported via highercontrol information and so on, the interference cancelation section 404separates the downlink signals for the subject terminal by canceling thedownlink signals for the other user terminals 20 that arenon-orthogonal-multiplexed. The downlink transmission data receivingsection 405 demodulates the downlink transmission data based on theseparated downlink signals for the subject terminal.

In this user terminal 20, when the downlink control informationreceiving section 401 receives a CQI (or CSI) feedback request, thechannel estimation section 402 calculates CQIs (or CSI) based on thedownlink reference signals transmitted in each transmission beam. Thecalculated CQIs (or CSI) are fed back to the radio base station 10 viathe feedback section 403.

The user terminal 20 acquires information for the subject terminal andinformation for the other user terminals 20 through, for example, highercontrol information. To be more specific, the user terminal 20 acquiresinformation to show the interference between the transmission beams, andinformation related to the other non-orthogonal-multiplexed userterminals 20. Based on these pieces of information, the interferencecancelation section 404 cancels the interference between thetransmission beams by using a linear filter such as MMSE and IRC, andcancels the interference by signals for the other user terminals thatare non-orthogonal-multiplexed in the same transmission beam. SIC isemployed to cancel signals for user terminals UE where the condition ofthe transmission path is poorer (the received SINR is lower or the pathloss is greater) than at the subject terminal. After having canceled theinterference by signals for the other user terminals UE, the downlinktransmission data receiving section 405 demodulates the downlinktransmission data for the subject terminal.

As described above, with the radio communication system 1 according tothe present embodiment, non-orthogonal multiplexing is applied toopportunistic beamforming that can achieve equivalent systemcharacteristics to MIMO transmission, so that it is possible to improvethe throughput and system capacity even more.

The present invention can be implemented with various corrections and invarious modifications, without departing from the spirit and scope ofthe present invention. That is to say, the descriptions herein areprovided only for the purpose of illustrating examples, and should by nomeans be construed to limit the present invention in any way.

The invention claimed is:
 1. A user terminal comprising: a receiver thatreceives: a signal subjected to multiplexing in a power dimension of agiven layer based on one or more transmitting antennas; and aninformation about the multiplexing in the power dimension of the givenlayer or one of the transmitting antennas, wherein the information aboutthe multiplexing in the power dimension comprises an interferencepresence information, and a processor that demodulates a signal for theuser terminal from the multiplexed signal based on the information aboutthe multiplexing in the power dimension and the interference presenceinformation, and determines a radio resource of an interfering signal inthe multiplexed signal to be the same as a radio resource of the signalfor the user terminal based on the interference presence information. 2.The user terminal according to claim 1, wherein the information aboutthe multiplexing in the power dimension represents a transmission powerratio.
 3. The user terminal according to claim 2, wherein a referencesignal included in the multiplexed signal has a reference signalstructure that is common to user terminals.
 4. The user terminalaccording to claim 2, wherein a reference signal included in themultiplexed signal is a cell-specific reference signal (CRS).
 5. Theuser terminal according to claim 2, wherein the multiplexed signal isfurther orthogonal-multiplexed in the given layer.
 6. The user terminalaccording to claim 1, wherein a reference signal included in themultiplexed signal has a reference signal structure that is common touser terminals.
 7. The user terminal according to claim 6, wherein thereference signal is specific to the given layer.
 8. The user terminalaccording to claim 7, wherein the reference signal is orthogonal to areference signal included in a signal that is multiplexed in the powerdimension in a different layer from the given layer.
 9. The userterminal according to claim 6, wherein the reference signal isorthogonal to a reference signal included in a signal that ismultiplexed in the power dimension in a different layer from the givenlayer.
 10. The user terminal according to claim 6, wherein the referencesignal is a channel state information reference signal (CSI-RS) or ademodulation reference signal (DM-RS).
 11. The user terminal accordingto claim 1, wherein a reference signal included in the multiplexedsignal is a cell-specific reference signal (CRS).
 12. The user terminalaccording to claim 1, wherein the multiplexed signal is furtherorthogonal-multiplexed in the given layer.
 13. A radio base station thatcommunicates with a user terminal, the radio base station comprising: aprocessor that multiplexes a signal in a power dimension of a givenlayer based on one or more transmitting antennas; and generatesinformation about multiplexing in the power dimension of the given layeror one of the transmitting antennas, wherein the information aboutmultiplexing in the power dimension comprises an interference presenceinformation, and a transmitter that transmits the multiplexed signal andtransmits the information about the multiplexing in the power dimensionto the user terminal for demodulation, wherein the user terminaldetermines a radio resource of an interfering signal in the multiplexedsignal to be the same as a radio resource of the signal for the userterminal based on the interference presence information.
 14. The radiobase station according to claim 13, wherein the processororthogonal-multiplexes the multiplexed signal.
 15. A radio communicationmethod for a user terminal comprising: receiving a signal subjected tomultiplexing in a power dimension of a given layer based on one or moretransmitting antennas and receiving information about the multiplexingin the power dimension of the given layer and the one or moretransmitting antennas, wherein the information about the multiplexing inthe power dimension comprises an interference presence information,demodulating a signal for the user terminal from the multiplexed signalbased on the information about the multiplexing in the power dimensionand the interference presence information, and determining a radioresource of an interfering signal in the multiplexed signal to be thesame as a radio resource of the signal for the user terminal based onthe interference presence information.